The present invention relates to an electromagnetic clutch control for vehicles, and more particularly to an electromagnetic control system which is capable of eliminating residual magnetism in the electromagnetic clutch by inverted clutch current passing a magnetizing coil, when change-gear in the transmission is in a neutral position and engine is not accelerated.
An electromagnetic clutch comprises an annular drive member secured to the crankshaft of an engine, a magnetizing coil provided in the drive member, a driven member secured to the input shaft of the transmission spaced by a small gap from the drive member, and a shift lever for changing the gear in the transmission. The shift lever is provided with a switch in the grip for the magnetizing coil, which is opened by operating pressure caused by manual operation of the shift lever, such as gripping pressure, pushing or pulling pressure. While the shift lever is being operated and operating pressure is exerted on the grip, the switch is opened with the result that the current does not flow through the magnetizing coil and the clutch is disengaged. When the shift lever reaches a gear engaging position and the operating pressure is removed, the switch is closed so that electric current flows through the magnetizing coil to magnetize the drive member. As the accelerator pedal is depressed, the current passing through the coil increases. The magnetic flux is aggregated in the gap between the drive member and the driven member, so that the driven member becomes coupled to the drive member. The clutch current passing the magnetizing coil is progressively increased according to the degree of depression of the accelerator pedal, while the clutch slips between the drive member and the driven member. Thus, the car may be smoothly and easily started by depressing the accelerator pedal without operating the clutch pedal. This is a well-known technique. In such an electromagnetic clutch, a so-called double clutch action is effected to thereby provide a smooth engagement between gears. Double-clutching is caused by the fact that when the operating pressure disappears at the neutral position during shifting operation of the shift lever, the shift lever switch is closed to engage the clutch.
In such a system, when the shift lever is shifted from one change speed position to another change speed position passing through the neutral position, the magnetism is able to remain in the clutch after cutting off of the clutch current because of magnetizing at the netural position. The shift lever must be operated against the drag torque caused by such residual magnetism, which requires a great manual operating force. This tendency increases when the engine speed is increased by depressing the accelerator pedal during idling of the engine at the start of the vehicle. In a transmission without a synchronizing mechanism, when gear-change is performed suddenly, the gears do not smoothly mesh each other, because it takes a long time for the gears to become synchronized.